The accumulation and sources of cytokinin and abscisic acid during the infection of corn (Zea mays) with Ustilago maydis

This thesis addresses the capability of Ustilago maydis to synthesize cytokinins [CKs], abscisic acid [ABA] and auxin [IAA] phytohormones and examines whether CKs and ABA are involved in the U. maydis-corn (Zea mays) infection process. Profiles of 12 different CKs and ABA in infected corn were compared to controls during a time-course following infection corresponding to symptoms at different infection stages. To examine whether the fungus was capable of producing these hormones; axenic cultures of the haploid and dikaryon forms of U. maydis were profiled by liquid chromatography-tandem mass spectrometry LC-(ES)MS/MS. Evidence shows CKs and ABA are elevated in leaves and stems of corn after infection; cisZR CK showed clear increases. It was also demonstrated that U. maydis is capable of producing IAA as well as significant quantities of CKs and ABA. This suggests that the elevation of CK and ABA in U. maydis infected corn tissue is possibly due to a fungal production and release of these phytohormones. This is the first study confirming the production of CKs and documenting the production of ABA by U. maydis . Also this is the first study to establish a relationship between these phytohormones and the U. maydis-corn (Zea mays ) infection.;Keywords: cytokinin, absicsic acid, auxin, phytopathology, Ustilago maydis, Zea mays, plant tumor physiology.